Theta role

A theta role is a semantic relation, such as agent or theme, that a predicate assigns to an argument. It captures the argument’s part in the event or state expressed by the predicate.

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Predicate: A linguistic expression that attributes a property or relation and can determine which arguments a sentence contains. A predicate assigns theta roles to the arguments it selects.
Theta criterion: A principle requiring each argument to bear one theta role and each theta role to be assigned to one argument. It formalizes the expected one-to-one relation between predicates’ roles and their arguments.
Agent (linguistics): The participant that intentionally initiates or controls an action. An agent is a common role assigned to the subject of an action predicate.
Grammatical relation: A syntactic relation such as subject or object that connects an expression to a sentence’s structure. A theta role describes meaning, while a grammatical relation describes syntactic position.
Argument (linguistics): An expression required or licensed by a predicate to complete its meaning. Theta roles describe the semantic contribution of each predicate argument.
Theta grid: A representation of the theta roles a predicate assigns to its arguments. A theta grid records a predicate’s role requirements before they are realized in a sentence.
Theme (linguistics): The participant that is moved, affected, or characterized in an event or state. A theme commonly fills the non-agent argument position of a predicate.
Case (grammar): A grammatical system that marks the roles of noun phrases through form or function words. Case can signal argument relations without being identical to a theta role.
Thematic relation: A semantic relation between a participant and an event or state, such as agent, patient, or instrument. Thematic relations are commonly used to characterize theta roles.
Thematic hierarchy: An ordering of thematic roles, often used to predict their mapping to grammatical positions. Hierarchies help explain why certain roles tend to map to subjects or objects.